Sealing device for pistons of rotary piston machines

ABSTRACT

A rotary piston machine wherein the piston has several lobes and orbits in the interior of a cylinder whereby its lobes sweep along the inner surface of the cylinder. The lobes are formed with axially parallel grooves bounded by internal surfaces of gear tooth shaped profile, and each groove receives a sealing element whose outer portion has a convex external surface engaging the inner surface of the cylinder and whose inner portion has several gear tooth shaped projections which are received with some clearance in complementary sections of the groove. Channels which are formed in the sealing elements establish communication between the chamber of the cylinder and certain sections of the grooves to insure that all sides the sealing elements are subjected to substantially identical pressures which are only slightly higher than necessary to maintain the sealing elements in requisite sealing engagement with the inner surface of the cylinder.

ilnite States set Stunner [21] Appl. No.: 73,039

[30] Foreign Application Priority Data Oct 2, 1969 Germany ..P 19 49695.8

[52] 115. CL ..418/l24, 418/179 [51] Int. Cl ..F0lc 19/02, F03c 3/00[58] Fieldo iSearch ..4l8/l24,123,113, 114,115, 41311 16, 117. 1 18.119, 120, 121, 122

[ 56] References Cited UNITED STATES PATENTS 3,120,921 2/1964 l-lovorka..4l8/116 X 3,323,498 6/1967 Krak et al. ..418/122 X FOREIGN PATENTS ORAPPLICATIONS 7 7 1,151,413 7/1963 Gennany ..418/124 PrimaryExaminer-Carlton R. Croyle Assistant Examiner-Richard E. GluckAttorney-Michael S. Striker [5 7] ABSTRACT A rotary piston machinewherein the piston has several lobes and orbits in the interior of acylinder whereby its lobes sweep along the inner surface of thecylinder. The lobes are formed with axially parallel grooves bounded byinternal surfaces of gear tooth shaped profile, and each groove receivesa sealing element whose outer portion has a convex external surfaceengaging the inner surface of the cylinder and whose inner portion hasseveral gear tooth shaped projections which are received with someclearance in complementary sections of the groove. Channels which areformed in the sealing elements establish communication between thechamber of the cylinder and certain sections of the grooves to insurethat all sides the sealing elements are subjected to substantiallyidentical pressures which are only slightly higher than necessary tomaintain the sealing elements in requisite sealing engagement with theinner surface of the cylinder.

7 12 Claims, 3 Drawing Figures SEALING DEVICE FOR PISTONS OF ROTARYPISTON MACHINES BACKGROUND OF THE INVENTION The present inventionrelates to improvements in rotary piston machines in general, and moreparticularly to improvements in sealing means which are interposedbetween the in temal surface of a cylinder and the external surface of apiston which orbits or rotates in the cylinder chamber.

It is already known to utilize in a rotary piston machine aneccentrically mounted rotary piston which comprises several cornerportions or lobes each of which sweeps along the internal surface of thecylinder when the piston is in motion. The lobes of the piston areprovided with sealing elements which must insure a satisfactory sealingaction between the inner surface of the cylinder (e.g., a surface havingan epitrochoidal or an analogous outline) and the external surfaces ofthe sealing elements.

German printed publication No. 1,151,413 discloses sealing elementswhich are intended for use in the lobes of the piston in a rotary pistonmachine. Each such sealing element has a substantially rectangularprofile and is inserted into an axially parallel groove provided in theexternal surface of the respective lobe. The sealing element has astrip-shaped outer portion which extends from the groove and is insealing engagement with the inner surface of the cylinder. That part ofthe sealing element which is received in the piston does not completelyfill the groove (either in the circumferential or in the radialdirection of the piston) to define with the piston a chamber which is incommunication with one of the compartments forming part of the internalspace of the cylinder and being separated from each other by the lobesof the piston. The chamber communicates with that compartment which ismaintained at the highest pressure. This is not entirely satisfactorybecause the sealing element is ressed against the inner surface of thecylinder with a force which is always much higher than the minimum forcerequired to establish a satisfactory seal between the external surfaceof the sealing element and the inner surface of the cylinder. Thus, thesealing element is biased outwardly by a pressure which alwayscorresponds to the maximum pressure in the interior of the cylinder,even if the sealing element is located in such angular position orpositions that a much lower pressure would suffice to ensure asatisfactory sealing action. The sealing action is even more pronouncedif the line of contact between the outer portion of the sealing elementand the inner surface of the cylinder is permitted to shift to one sideof the groove. If the sealing element happens to travel in an area whichis maintained at a relatively low pressure, its external surface issubjected to a relatively low pressure which is but a fraction of thepressure in the chamber. Therefore, the outer portion of the sealingelement is likely to be pressed against the cylinder with a force whichsuffices to destroy the film of lubricant along the inner surface of thecylinder. Once the lubricant film is destroyed, the metallic material ofthe sealing element comes into direct contact with the metallic materialof the cylinder to generate excessive friction and wear and to causepremature destruction of the sealing element.

SUMMARY OF THE INVENTION An object of the invention is to provide anovel piston for rotary piston machines and to provide the piston withnovel and improved sealing elements.

Another object of the invention is to provide a sealing element which isconfigurated and mounted in the piston of a rotary piston machine insuch a way that the force with which it is urged against the cylinder ofthe machine when the piston rotates exceeds only slightly the minimumforce which is required to insure a satisfactory sealing action.

An additional object of the invention is to provide a sealing elementwhich is constructed and mounted with a view to avoid destruction of thefilm of lubricant along the inner surface of the cylinder in a rotarypiston machine.

Still another object of the invention is to provide a sealing elementwhich can be readily installed in the pistons of presently known rotarypiston engines without necessitating appreciable alterations in thedesign of such pistons.

The invention is embodied in a rotary piston machine which comprises acylinder having a chamber and including an inner surface which surroundsthe chamber and preferably comprises two main arcuate sections, a pistonwhich is installed in the cylinder chamber for rotation about apredetermined axis and is provided with several circumferentially spacedlobes sweeping along the inner surface of the cylinder when the pistonrotates, an axially parallel groove provided in each lobe of the pistonand being surrounded by an internal surface of gear tooth shapedprofile, and a metallic or plastic sealing element in each groove. Eachsealing element includes an outer portion having a convex externalsurface at least a portion of which is preferably of a circularcylindrical outline and is in sealing engagement with the inner surfaceof the cylinder to divide the chamber into a pair of compartments, andan inner portion having at least two gear tooth shaped projections whichare received in the respective groove. Each sealing element is furtherprovided with substantially radially extending channel means locatedbetween the projections of its inner portion and connecting thecorresponding groove with one of the compartments to thus insure thatthe pressure against the surface of the inner portion of each sealingelement does not excessively deviate from the pressure which actsagainst the external surface of the outer portion of each sealingelement.

The sealing elements may be made of a metallic material (e.g.,hardenable steel) or from a suitable synthetic plastic material (such aspolytetrafluorethylene or another material which is resistant to wearand has a low coefficient of friction The metallic sealing elements arepreferably made by drawing or precision rolling a ductile metallicmaterial to form an elongated blank and by subdividing the blank intodiscrete sealing elements which can be surface-hardened by nitration orby an inductive hardening process. Plastic sealing elements can beproduced by extrusion or in the cavity of a suitable mold.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved sealing device itself, however, both as to its construction andthe method of making and mounting the same, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary transversesectional view of a rotary piston machine whose piston is provided withsealing elements embodying one form of the invention;

FIG. 2 is a similar view of a second rotary piston machine whose pistonis provided with modified sealing elements and FIG. 3 is a sectionalview of the entire rotary piston machine which embodies the structureshown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 3 illustrate arotary piston machine, e.g., an internal combustion engine, including acylinder 101 having inner surface 2 which is of epitrochoidal or similaroutline and has two main arcuate portions. The internal chamber of thecylinder 101, which is surrounded by the inner surface 2, accommodatesan eccentrically mounted piston I which travels about a predeterminedaxis and comprises several (for example, three) axially parallel cornerportions or lobes which sweep along the inner surface 2 when the piston1 rotates. One such corner portion or lobe of the piston 1 is shown indetail in FIG. 1; it is provided with an axially parallel groove 10 ofgear tooth shaped outline. In the embodiment of FIG. I, the groove 10has two outwardly diverging sections 10a each of which extends inparallelism with the axis of the piston 1. The groove 10 receives anovel sealing element 3 having an outer portion bounded by a convexexternal surface 6 which sealingly engages the inner surface 2 to dividethe chamber of the cylinder 101 into compartments 4 and 5. The surface 6preferably forms part of a circular cylindrical surface and its endportions (as considered in the direction of rotation of the piston 1)are flush with the adjacent portions 7 of the outer surface of theillustrated lobe. Thus, the radius of curvature r of the externalsurface 6 is such that it ensures tangential transition of the ends ofthis surface into the surfaces 7. FIG. 3 shows that the inner surface 2of the cylinder 10] has two main arcuate sections.

The inner portion of the sealing element 3 comprises two gear toothshaped axially parallel projections 8 each of which is received in oneof the sections 10a of the groove 10. The flanks of each projection 8make an angle alpha which, in FIG. I, at least approximates 30, and thetips or top lands of the projections 8 are flat, as at 8a. The anglealpha is preferably between 30 and 60. The surface of the inner portionof the sealing element 3 between the adjacent flanks of the projections8 is concave, as at 8b.

The sealing element 3 is further provided with a row of radiallyextending bores or passages 9 which communicate with the groove 10in theregion between the projections 8 and with one of the compartments 4, 5.The row of passages 9 is parallel to the axis of rotation of thepiston 1. Each section 10a of the groove 10 has an inner end portionwhich is bounded by a concave surface, as at 1%. It is to be noted thateach lobe of the piston 1 is provided with a groove 10 for a discretesealing element 3.

Each end face of the piston 1 is further provided with straight recessesor cutouts 1a for inclined sealing strips 11 which bear against theadjacent inner end faces of the cylinder 101. The strips 11 are mountedon springs (not shown) located in the innermost portions of therespective cutouts 1a so that the outer portions of the strips arebiased against the cylinder. It is also possible to make the strips ofelastically deformable material. The purpose of the sealing strips 11 isto seal the compartments in the chamber of the cylinder from each otherin the region of the respective end faces of the piston 1. The endportions of each sealing strip 11 abut at an obtuse angle against twosealing elements 3.

The sealing elements 3 are mounted in the respective grooves 10 with acertain minimal clearance so that, when the piston I rotates in thedirection indicated by the arrow 13, the front or right-hand flanks ofthe projections 100 can respectively move away from the adjacentportions of the internal surface of the piston 1 to define narrow gaps12 and 12a. Such gaps develop in response to friction between the convexsurfaces 6 of the sealing elements 3 and the internal surface 2 of thecylinder 101. The left-hand or trailing flanks of the projections 10aabut against and are in sealing engagement with the adjacent portions ofthe internal surface in the piston 1. The gap 12 is in directcommunication with the compartment 4. The other gap 12a communicateswith the compartment by way of the passages 9. The pressure in thecompartment 4 is the same as in the front section We of the groovetherefore, all sides of that part of the sealing element 3 which islocated to the right of the line of contact between the surfaces 2 and6, as viewed in FIG. 1, are subjected to a uniform pressure. The rearpart of the sealing element 3 (to the left of the line of contactbetween the surfaces 2 and 6) is subjected to a uniform pressure becausethe passages 9 communicate with the chamber 5. It will be seen that, inthe position of the sealing element 3 as shown in FIG. 1, the pressureacting against the left-hand part of the surface 6 is the same as thepressure which acts on the adjacent projection 8 along the gap 12a andin the innermost part of the respective section 10a. When the passages 9are sealed from that compartment which is maintained at a higherpressure, the total area of the surface of the sealing element 3 whichis subjected to higher pressure is reduced accordingly because the gap12 or 12a then communicates with the compartment which is maintained atthe lower pressure. It can be said that the area of the internal surfaceof the sealing element 3 which is subjected to pressure is reduced whenthe pressure acts against a smaller part of the external surface 6, andvice versa. However, there always remains a surplus force or pressurewhich acts between those flanks of the projections 8 which are incontact with the piston l and the respective portions of the surfacebounding the groove 10. The magnitude of such surplus pressure isdetermined by the parameter B. The surplus pressure ensures that thesealing element 3 is held in requisite sealing engagement with the innersurface 2. The parameter E can be defined as the normal or averagedistance between a first plane which includes the trailing flank of thefront projection 8 and a second plane which is parallel to the firstplane and includes the line of contact between the surfaces 2 and 6.

The just described construction and mounting of the sealing element 3ensure that the pressure between the surfaces 2 and 6 remains relativelylow so as not to destroy the film of lubricant on the surface 2.

It will be understood that the pressure in the compartments 4 and 5varies, i.e., that the pressure in the compartment 4 at times exceedsand is at times less than the pressure in the compartment 5. Therefore,the sealing element 3 of FIG. 1 moves in the groove 10 between theillustrated position (when the pressure in the compartment 4 exceeds thepressure in the compartment 5) and a second position in which theright-hand flanks of the projections 8 abut against the adjacentsurfaces in the respective sections 10a of the groove 10 (namely, whenthe pressure in the compartment 5 exceeds that in the compartment 4).This does not affect the aforedescribed advantageous characteristics ofthe sealing element 3 i.e., this sealing element then also ensures arequisite sealing action between the compartments 4 and 5 by exertion ofa relatively low pressure against the surface 2. The gaps 12, 12a arethen adjacent to the left-hand surfaces in the sections 10a.

The sealing element 3 moves between the two positions when the pressurein the compartment 4 nearly equals the pressure in the compartment 5.This is the stage of temporary absence of complete sealing action but itdoes not affect the operation of the rotary piston machine because thepressures in the compartments 4, 5 are then substantially identical.

Since the convex external surface 6 of the sealing element exhibits arather small curvature (it preferably forms part of a circularcylindrical surface, at least in the region where it touches the surface2), its configuration deviates only slightly from that of the innersurface 2 of the cylinder 101. Also, since the line of contact betweenthe surfaces 2 and 6 is always located between the ends of the sealingelement 3, as considered in the circumferential direction of the piston1, only a portion of the surface 6 is subjected to high pressures at anytime. These features ensure that the magnitude of surplus forces whichurge the sealing element 3 against the surface surrounding the groove 10of the piston 1 can be maintained within a rather low range.

Referring to FIG. 2, the cylinder 101 cooperates with a modified piston1' having in each of its corner portions or lobes an axially parallelgroove 10' which includes four outwardly diverging axially parallelsections 10a. The inner portion of the sealing element 3' has fourprojections 8' each of which extends into one of the sections 10a. Theexternal surface 6' of the sealing element 3' engages the innersurface 2of the cylinder 101 to separate the compartments 4 and 5 from eachother. The sealing element 3 is formed with three axially parallel rowsof radially extending bores or passages 9' which respectivelycommunicate with the second, third, and fourth sections 10a (asconsidered in the direction of rotation of the piston 1'--indicated bythe arrow 13).

The sealing element 3 allows for an even more precise gradation ofrelieved and pressurized surfaces. When the piston 1 rotates in thedirection indicated by the arrow 13, the projections 8 of the innerportion of the sealing element 3' define four clearances or gaps 12,12a, 12b, 12C. The number of projections on a sealing element depends onthe size of the piston and on the dimensions and configuration of itslobes. If the nature of the operation of the rotary piston machinerequires it, the sealing elements can be formed with a very large numberof projections to ensure that the pressure between the external surfaceof each sealing element and the inner surface of the cylinder is alwayssumcient but does not substantially exceed the maximum desirablepressure.

Another important advantaGe of the improved sealing elements is thattheir characteristic mass is low (about 1/10) so that the sealingelements are subjected to relatively small centrifugal forces. Suchcentrifugal forces tend to press the sealing elements against the innersurface of the cylinder. Therefore, a piston which employs the improvedsealing elements can be used with advantage in high-speed rotary pistonengines. It is clear, however, that the sealing elements of the presentinvention can be used with equal advantage in many other types of radialpiston machines, such as hydraulic machines, compressors, vacuum pumps,or other types of pumps, steam engines and/or others.

The sealing elements 3 or 3 may consist of a metallic material, such ashardenable steel, or of a suitable wear-resistant synthetic plasticmaterial having a relatively low coefficient of friction (for example,polytetrafluorethylene). If the sealing elements consist of a syntheticplastic material, they can be reinforced by the addition of filamentarymaterials such as glass, carbon or asbestos fibers.

If the sealing elements consist of a metallic material, they may beproduced by a precision-rolling or drawing method. The surfaces of thethus obtained sealing elements can be hardened inductively or bynitration. If the sealing elements consist of a synthetic plasticmaterial, they can be produced by extrusion or in the cavities ofsuitable molds. The precisionrolling, drawing or extruding methodinvolves forming elongated blanks and severing the blanks to yieldsealing elements of desired length.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of my contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

Iclaim:

1. In a rotary piston machine, a combination comprising a cylinderhaving a chamber and including an inner surface surrounding saidchamber, a piston installed in said chamber for rotation about apredetermined axis and having a plurality of circumferentially spacedlobes arranged to sweep along said inner surface in response to rotationof the piston, each of said lobes having a substantially axiallyextending groove surrounded by a gear tooth shaped internal surface; andsealing elements provided in said grooves, each sealing elementincluding an outer portion having a convex external surface abuttingagainst said inner surface to divide said chamber into a pair ofcompartments and an inner portion having at least two substantially geartooth shaped projections received in the respective groove, each sealingelement further having channel means located between the projections ofthe respective inner portion and connecting the corresponding groovewith one of said compartments.

2. A combination as defined in claim 1, wherein the number of lobes onsaid piston exceeds two and wherein the inner surface of said cylinderconsists of several arcuate portions.

3. A combination as defined in claim 1, wherein at least a portion ofeach of said external surfaces forms part of a cylindrical surface andwherein said piston has an external surface portions of which flank saidgrooves and are flush with the adjacent portions of the respectiveexternal surfaces.

4. A combination as defined in claim 3, wherein said portion of saidexternal surface of each sealing element forms part of a circularcylindrical surface and wherein said portion of such external surfaceengages said inner surface.

5. A combination as defined in claim 1, wherein each of said projectionshas two mutually inclined flanks making an angle of 30- 60.

6. A combination as defined in claim 1, wherein each of said grooves hasa plurality of sections, one for each of said projections, and each ofsaid internal surfaces has a concave portion in the bottom part of eachof said sections, each of said projections extending into its respectivesection.

7. A combination as defined in claim 1, wherein each of said innerportions is received with clearance in the respective groove and whereineach of said projections has two mutually inclined flanks, saidclearance consisting of a plurality of gaps provided between saidinternal surfaces and one flank of each of said projections.

8. A combination as defined in claim 1, wherein said sealing elementsconsist of metallic material.

9. A combination as defined in claim 8, wherein said metallic materialis hardenable steel.

10. A combination as defined in claim 1, wherein said sealing elementsconsist of wear-resistant synthetic plastic material having a lowcoefficient of friction.

11. A combination as defined in claim 10, wherein said synthetic plasticmaterial is polytetrafluorethylene.

12. A combination as defined in claim 10, wherein said synthetic plasticmaterial contains reinforcing inserts selected from the group consistingof glass, carbon and asbestos fibers.

1. In a rotary piston machine, a combination comprising a cylinderhaving a chamber and including an inner surface surrounding saidchamber, a piston installed in said chamber for rotation about apredetermined axis and having a plurality of circumferentially spacedlobes arranged to sweep along said inner surface in response to rotationof the piston, each of said lobes having a substantially axiallyextending groove surrounded by a gear tooth shaped internal surface; andsealing elements provided in said grooves, each sealing elementincluding an outer portion having a convex external surface abuttingagainst said inner surface to divide said chamber into a pair ofcompartments and an inner portion having at least two substantially geartooth shaped projections received in the respective groove, each sealingelement further having channel means located between the projections ofthe respective inner portion and connecting the corresponding groovewith one of said compartments.
 2. A combination as defined in claim 1,wherein the number of lobes on said piston exceeds two and wherein theinner surface of said cylinder consists of several arcuate portions. 3.A combination as defined in claim 1, wherein at least a portion of eachof said external surfaces forms part of a cylindrical surface andwherein said piston has an external surface portions of which flank saidgrooves and are flush with the adjacent portions of the respectiveexternal surfaces.
 4. A combination as defined in claim 3, wherein saidportion of said external surface of each sealing element forms part of acircular cylindrical surface and wherein said portion of such externalsurface engages said inner surface.
 5. A combination as defined in claim1, wherein each of said projections has two mutually inclined flanksmaking an angle of 30*- 60*.
 6. A combination as defined in claim 1,wherein each of said grooves has a plurality of sections, one for eachof said projections, and each of said internal surfaces has a concaveportion in the bottom part of each of said sections, each of saidprojections extending into its respective section.
 7. A combination asdefined in claim 1, wherein each of said inner portions is received withclearance in the respective groove and wherein each of said projectionshas two mutually inclined flanks, said clearance consisting of aplurality of gaps provided between said internal surfaces and one flankof each of said projections.
 8. A combination as defined in claim 1,wherein said sealing elements consist of metallic material.
 9. Acombination as defined in claim 8, wherein said metallic material ishardenable steel.
 10. A combinaTion as defined in claim 1, wherein saidsealing elements consist of wear-resistant synthetic plastic materialhaving a low coefficient of friction.
 11. A combination as defined inclaim 10, wherein said synthetic plastic material ispolytetrafluorethylene.
 12. A combination as defined in claim 10,wherein said synthetic plastic material contains reinforcing insertsselected from the group consisting of glass, carbon and asbestos fibers.